The present invention relates to an automotive vehicle electronic meter, and more particularly to a control circuit therefor.
Electronic meters used in automotive vehicles indicate, in bar form or by digital display, various information such as remaining fuel amount, cooling water temperature, hydraulic pressure, and battery voltage, and include fluorescent display tubes, liquid crystal displays.
Such information is commonly sensed as voltage signals dependent on the resistance values of various sensors. The battery voltage is directly sensed. These sensed voltage signals are subjected to processes such as analog to digital conversion and are then displayed.
When the vehicle is to be started, the load on the starter motor lowers the battery voltage. For instance, the output of a conventional 12-volt battery lowers to 5-8 volts when starting.
In an electronic meter such as mentioned above, the lowering of the battery voltage causes fluctuations in the sensed signal voltages, flickering displays and incorrect indications.
If the power supply for an electronic display meter is taken from an accessory terminal of an ignition switch, the meter indication will disappear and thus be free from incorrect display because the accessory terminal is not supplied with electric power when the ignition key is rotated to the starter position. Under these conditions, when the side marker lamps, tail lamps and so forth are lighted by turning on the light switch with the ignition key still in the off position, or with the key not inserted, illumination lamps for the meters within the instrument panel are also turned on, but the electronic meter remains off, displaying nothing, so that it appears odd among other lighted meters and presents an undesirable appearance thereby reducing the value of the vehicle. Therefore, it is desirable that the electronic meter should operate both when the light switch is turned on and when the accessory circuit is operated by the ignition switch. If, however, the electronic meter is operated whenever the light switch is turned on, the electronic meter will indicate a measured value during engine starting so that the meter indication will flicker or be incorrect.